The trend is for car battery prices to fall 35% every 10 years. Imagine they fall only 70% in the next 25.

The trend is for oil prices to rise. Given that output is already falling, and will be less than half of current levels by 2037, and given the growing demand in China/ East Asia/ South Asia you describe... If there was no substitution away from oil, prices would probably rise towards 300$/ barrel in this timeframe.

That is, battery costs might fall from $0.37/mile today, to $0.11/mile. Electricity prices might rise from $0.06/mile to $0.15. That's a 2037 (probable overestimate) of $0.26 for an average vehicle.

On the other hand, gas (petrol) prices would rise from $0.25/mile today to more than $0.50/mile.

In other words, don't expect oil prices to get so high. Don't expect all those extra cars to cause so much extra pollution. Within the 20 year time frame you describe, there will come a point when electric cars are cheapest, and combustion cars are a luxury (likely, highly regulated and highly taxed).

If you are motivated be broader environmental concerns, you might be worried by all that coal that China will be burning to generate the electricity. Yet, that isn't a concern for air pollution - already, all new coal plants are fitted with modern scrubbers & filters - they only really emit CO2 and water vapour.